As is commonly known, an electric power steering apparatus is configured so as to detect a steering torque applied by a driver to a steering wheel, and cause an electric motor to generate an assist torque commensurate with the detected steering torque, thereby assisting the steering of the driver.
To date, as this kind of electric power steering apparatus, there is an electric power steering apparatus configured so that two sets of independent stator windings are provided in an electric motor, two sets of inverter circuits that can independently drive the two sets of stator windings are provided in a control unit, and the stator windings are individually controlled in concert by the corresponding inverter circuits. This kind of existing electric power steering apparatus is configured so that when an abnormality occurs in one set of stator windings and inverter circuits, driving of the motor is continued using only a normal set formed of the other stator windings and inverter circuits.
Furthermore, there is also an existing electric power steering apparatus such that a failure is more thoroughly prepared for by portions of a control unit other than an inverter circuit also being a double system (for example, refer to Patent Document 1). The existing electric power steering apparatus disclosed in Patent Document 1 is configured to include two sets each of a connection terminal connected to a positive electrode side terminal +B of a battery acting as an external power supply mounted in a vehicle, an input circuit, a CPU (central processing unit), an output circuit, and the like, which form one portion of components of the control unit, and when an abnormality occurs in one of the two sets, motor control can be continued on the other, normal side.